The concept of 'nudging' involves changing people's behaviour without banning anything or significantly changing the financial impact of choices.

Health secretary Andrew Lansley has said that governments should not legislate to restrict people's food choices and lifestyles.

In July 2010, he set out plans for public health to be based on local initiatives designed to achieve outcomes targets.

But Cambridge University researchers argue that, while nudging can alter behaviour, it often moves people towards unhealthy choices.

There is little evidence to support the effectiveness of nudging improving population health and reduce health inequalities, they said.

'Effective nudging may require legislation, either to implement healthy nudges ... or to prevent unhealthy nudges from the industry,' they added.

A DoH spokesman said it was clear that 'the old ways of tackling public health problems have not always delivered the necessary improvements'.

'Our approach to public health follows a model that means we will employ a range of approaches to improve health - from nudging when appropriate to more serious interventions, such as legislation, when necessary,' he said.

The Faculty of Health said GPs already nudge people when they advocate healthy eating and exercise.